Ancient/Classical History/Romans citizens
How did Romans prove their citizenship in ancient Rome?
as far as we know, the ancient Romans proved their citizenship (Latin, “Ius civitatis” = right of citizenship) by a kind of wooden diptych/tablet called “syngraphus”, which acted as a certificate of citizenship,i.e. a passport, as we read in a comedy by Plautus entitled “Captivi” (“The Captives”/The Prisoners”), Act 2, Scene 3, line 90, and Act 3, Scene 2, line 6, where a comedy’s character named Hegio asks for a passport from the prætor so that another person may be allowed to go home.
So, since the great Roman comic dramatist Plautus was born in 254 BC and died in 184 BC, we can say that the noun “syngraphus”, just meaning “passport”, was already used in those times.
Proof of citizenship could therefore be determined through reference to the census archives (“tabularia”, in Latin) where the name of every citizen was kept, or through the presentation of the diptych ("syngraphus"), just used as a passport.
Citizenship lists were of course maintained by the magistrates (called “praetores” and “censores”, in Latin)first in Rome and then all over the Roman empire which lasted until 476 AD, the city of Rome having been founded in 753 BC.